The present application relates generally to materials for installation in outdoor fields such as sports fields, playgrounds, and the like, for providing shock absorption for persons engaged in activities on the field and for facilitating drainage of rainfall from the field.
In an outdoor field of the above-noted type, typically the earth substrate is first graded to a suitable slope that will allow water to drain toward drain pipes installed in certain locations adjacent the field. A drainage layer (e.g., an aggregate such as gravel) is installed above the earth substrate, and a shock-absorbing layer is then installed above the drainage layer. A synthetic turf product can then be installed atop the shock-absorbing layer. There are many variations of such installations, but a common factor among many of them is the substantial labor and time required for installing them, which is due in large part to the complexity of having separate drainage and shock-absorbing components that must be installed sequentially.
Attempts have been made to provide a unitary drainage and shock-absorbing device for outdoor field installations, although with limited success. For example, U.S. Patent Application Publication 2005/0238433 published on Oct. 27, 2005 describes one embodiment of a drainage blanket consisting of a core having a base and a plurality of upstanding cup-like studs extending therefrom, a top sheet covering the top of the core, two side sheets on opposite side edges of the core, and an optional bottom sheet on the bottom of the core. The top sheet has holes that allow water to drain into the core, where the water can then flow horizontally through the spaces between the studs, the water exiting through passages at the ends of the drainage blanket. The '433 publication describes another exemplary embodiment of the drainage blanket as consisting of a high-density polyethylene core of fused, entangled filaments sandwiched between a needle-punched non-woven geotextile on one side and a head-bonded non-woven geotextile on the other side. The '433 publication further indicates that the drainage blanket can be constructed to provide shock attenuation, but includes no description as to how to do so, particularly for an installation such as a sports field where adequate shock attenuation is especially critical.
The complexity of construction of the drainage blankets described in the '433 publication would be expected to make them too costly for practical use in outdoor field installations of large dimensions. The embodiment having the core with upstanding studs and a geotextile top sheet is believed to be commercialized under the trademark PRODRAIN™ by Global Synthetics. The ProDrain 6000 and ProDrain CD12 products have thicknesses of 10 and 12 mm, respectively, and come in widths of about 1 meter and lengths of 15 meters and 25 meters, respectively, which lengths presumably are the practical upper limit for the manufacturing process by which the products are made. These lengths are too short for covering the entire width of a sports field such as a soccer field, and therefore multiple pieces would be required to span the width of the field, and thus seams would be needed. Furthermore, these products would not provide the degree of shock absorption needed in a sports field because the core is a molded impervious plastic article of high crush-resistance.
U.S. Pat. No. 6,818,274 describes an artificial turf system that in one embodiment includes a shock-attenuating pad that includes one or more drainage channels in its lower surface. The pad is described as being a recycled closed-cell polyethylene foam sheet. Such a foam sheet is formed of shredded particles of polyethylene foam that are bonded together to form the sheet. Vertical drainage through such a sheet depends entirely on the interstitial spaces between the foam particles, which means that it is difficult to precisely tailor the vertical drainage performance of the sheet to meet a given vertical drainage requirement. Also, some water will pass through portions of the sheet in between the drainage channels and will have to flow between the bottom surface of the sheet and the substrate in order to reach one of the drainage channels, which is undesirable. Shock absorption and thickness across the area of the recycled foam sheet tends to be somewhat non-uniform because of the bonded-particle construction of the sheet and the fact that the particles are of different densities and material composition. This results in non-uniform expansion and/or contraction of the particles during sheet construction. Additionally, the recycled foam sheet has a relatively high basis weight and thus in long lengths is somewhat difficult to handle and maneuver on the installation site.
What is needed is a unitary shock and drainage pad for outdoor field installations that provides excellent drainage and shock absorption, that has a uniform thickness and uniform shock-absorption properties across its area, and that can be economically manufactured in any desired length (i.e., a roll-form shock and drainage pad) so as to reduce the number of seams needed in a large field installation. A reduced basis weight relative to the above-described recycled foam sheet is also desirable.